Electronic device manufacturers strive to produce a rich interface for users. Conventional devices use visual and auditory cues to provide feedback to a user. In some interface devices, kinesthetic feedback (such as active and resistive force feedback) and/or tactile feedback (such as vibration, texture, and heat) is also provided to the user, more generally known collectively as “haptic feedback.” Haptic feedback can provide cues that enhance and simplify the user interface. Specifically, vibration effects, or vibrotactile haptic effects, may be useful in providing cues to users of electronic devices to alert the user to specific events, or provide realistic feedback to create greater sensory immersion within a simulated or virtual environment.
Haptic feedback has also been increasingly incorporated in portable electronic devices, such as cellular telephones, personal digital assistants (PDAs), portable gaming devices, and a variety of other portable electronic devices. For example, some portable gaming applications are capable of vibrating in a manner similar to control devices (e.g., joysticks, etc.) used with larger-scale gaming systems that are configured to provide haptic feedback. Additionally, devices such as cellular telephones and PDAs are capable of providing various alerts to users by way of vibrations. For example, a cellular telephone can alert a user to an incoming telephone call by vibrating. Similarly, a PDA can alert a user to a scheduled calendar item or provide a user with a reminder for a “to do” list item or calendar appointment.
In many devices, an actuator is used to create the vibrations that comprise some haptic effects. One type of actuator that is frequently used in portable electronic devices is a Linear Resonant Actuator (“LRA”). Typically, an LRA requires a bidirectional signal (i.e., an alternating positive voltage and negative voltage signal) in order to create the desired vibrations. However, most portable electronic devices generate direct current only, so that a special drive circuit is required to generate the bidirectional signal. The typical circuit includes a H-bridge, which is a circuit that includes four switches. However, for portable devices, cost is an important driving factor, and the cost of four switches may be proportionally high relative to the rest of the portable device.
Based on the foregoing, there is a need for a less expensive actuator and drive circuit for generating haptic effects.